lib: add comment to script eval _tickCallback
PR'ing this so it doesn't get forgotten, see https://github.com/nodejs/node/pull/11958#discussion_r107184672
Add a comment to match lib/module.js, missed in #11958.
Refs: https://github.com/nodejs/node/pull/11958
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
commit message follows [commit guidelines][]
Affected core subsystem(s)
lib
cc/ @Fishrock123 @bnoordhuis @jasnell